1. Field of the Invention
The present invention relates generally to laminated materials comprising a layer of nonwoven fabric which is capable of absorbing liquids and a layer of plastic film which is impermeable to liquids. More particularly, the invention relates to laminated materials having improved resistance to "linting", which is loss of fiber from the nonwoven fabric portion of the laminate during handling or use thereof. Even more particularly, the invention relates to laminated materials which can be advantageously used as reinforcing materials for surgical drapes. Surgical drapes employing the laminated material of the present invention have increased structural integrity in the region where the laminate is used; good absorption of liquids such as water, blood, alcohol, and the like, which are commonly encountered during surgery; and a significantly reduced tendency to "lint" or shed fibers or fiber fragments during handling or use. The latter feature is particularly important in view of the desire to prevent to the extent possible foreign materials such as fibers or fiber fragments, from reaching the surgical site.
2. Description of the Related Art
Disposable surgical drapes comprising main sheets of plastic film or nonwoven fabric have been known and used for a number of years. These drapes, which are generally supplied to the end-user in a sterilized condition, are large enough to cover the patient about to undergo surgery and to extend over the sides and usually one end of the operating table toward the floor. Such draping of the patient and operating table provides a "sterile field" and helps isolate the patient from undesirable contamination by foreign materials.
Disposable surgical drapes are very often fenestrated; i.e., they are provided with a fenestration or opening through which the surgery is actually performed. Such fenestrations are usually provided at the time of manufacture of the drape. Some surgical drapes, however, are not provided with a fenestration at the time of manufacture. In such instances, a member of the surgical team will provide a fenestration by cutting away portions of the drape at the region where it is desired to have the fenestration.
It is also known, especially where the main sheet of a surgical drape comprises a nonwoven fabric, to provide the drape with a reinforcing panel in the region surrounding the aforementioned fenestration or the region where such fenestration will be made by the surgical team. Prior art reinforcing materials or panels have utilized a layer of absorbent material, such as a nonwoven fabric, foam or tissue, laminated to a layer of liquid impermeable material such as polyethylene film. The reinforcing material is secured to the upper surface of the main sheet of the drape around the site of the fenestration so that its liquid impermeable layer faces the main sheet and its absorbent layer remains exposed so that it will face upwardly when the patient is draped. The reinforcing panel itself has typically been secured to the main sheet by the use of a continuous layer of a suitable adhesive.
A surgical drape having a reinforcing panel of the type just described has improved structural integrity resulting from the fact that there are additional layers of material in the reinforced region and because of the presence of the fluid impermeable plastic film layer in the reinforcing panel. The absorptive upper surface of the reinforcing panel serves to absorb and retain the various liquids, such as blood and irrigating fluids, which are encountered at the surgical site and prevent the same from pooling on the drape or running from the surface thereof onto the floor or the clothing of the medical personnel in attendance. Additionally, the liquid impervious layer of the reinforcing panel prevents liquids which are captured by the absorbent layer from undesirably penetrating the underlying portion of the main sheet of the drape and contacting the body of the patient.
One prior art method which has been used to make the reinforcing panel is extrusion lamination, in which the liquid-impermeable material, e.g. polyethylene, is extruded directly onto one major surface of the liquid absorbent layer. Typically, lamination is accomplished at temperatures in the range 450.degree.-550.degree. F. (232.degree.-288.degree. C.), with nip pressures between 20 and 50 lb/in.sup.2 (138-345 kN/m.sup.2). The surface fibers comprising the absorbent layer are coated with and become embedded in the extruded polyethylene layer, thereby forming a laminated material in which the liquid absorbent layer is secured to the liquid impermeable layer.
In another prior art method of making a reinforcing panel (adhesion lamination), a layer of pressure-sensitive adhesive is applied to one surface of either the absorbent layer or the liquid-impermeable layer and the two layers are fed through the nip of a pair of pressure rollers at ambient temperature. The layers are typically laminated at nip pressures of 10-20 lb/in.sup.2 (69-138 kN/m.sup.2).
Preparation of reinforcing panels by the aforementioned prior art methods tends to undesirably stiffen the panel and reduce the liquid absorbing capacity of the absorbent layer. This is because some of the fibers constituting the absorbent layer are embedded in or are partially or fully coated by the material used for the liquid-impermeable layer and/or by the adhesive.
A decrease in the absorptive capacity of the reinforcing panel is undesirable in that it tends to reduce the ability of the drape to control fluids at the operative site and because it may, in extreme cases, lead to pooling of fluids on the surface of the drape. In addition, many reinforcing panels contain an antimicrobial agent to kill microbes which may be carried in body fluids, irrigating fluids and the like encountered during surgery. These microbes are killed when the liquids carrying them are brought into contact with the antimicrobial agent in the absorbent layer of the reinforcing panel. Thus, if the absorbency of the reinforcing panel is reduced, the bacteria may not be brought as quickly into contact with the bacteriocidal agent and the bacteria may not be killed as quickly as would otherwise be possible.
Another problem which has been experienced with reinforcing panels of the prior art is that known as "linting". This is the shedding, during pre-operative handling or actual use of the drape, of fibers or fiber fragments from the absorbent layer comprising the reinforcing panel. It is, of course, desirable to minimize linting in order to keep foreign particles from contaminating the environs of the operating room or the site of the surgical incision.